1. Field of the Invention
This invention relates to a thin film electroluminescence (hereinafter referred to as EL) device which can be used as an EL display.
2. Discussion of Background
An EL device is currently utilized as a flat pannel display which has a large capacity and is capable of representing visible images of high quality.
The EL device is typically fabricated in such a manner that a transparent electrode layer, a first insulating layer, an EL emitting layer, a second insulating layer and a back electrode layer are succesively formed on a substrate of transparent glass in the mentioned order. The EL device entirely consists of solid materials, so that it has high mechanical strength and enviromental resistance, and therefore the EL device is suitable for use as the display of portable word processors and computers.
Typical examples of host materials for a multi-color EL device are alkali earth metal sulfides such as SrS and CaS, and alkali earth metal selenides such as SrSe and CaSe. However, an EL device which comprises an EL emitting layer containing such a host material cannot maintain high reliability for a prolonged period.
In order to overcome the above drawback of the conventional EL devices, it has been proposed to employ a nitride layer as an insulating layer as disclosed in Japanese Laid-Open Patent Application No. 62-5596 and Japanese Patent Application No. 60-228863. However, detailed studies on the nitride insulating layer, especially, with respect to the crystallinity of the nitride and the thickness of the layer, have never been made so far, and it has only been known that amorphous layers are preferable as the insulating layer. An EL device which comprises an amorphous nitride layer as an insulating layer emits weak EL and has unsatisfactory breakdown strength.
Japanese Laid-open Patent Application No. 61-198592 discloses an EL device comprising a transparent electrode layer made of a C-axis oriented zinc oxide. However, when an alkali earth chalcogen compound is used as a host material, the EL device cannot maintain high reliability for a prolonged period.
Further, an insulating layer containing a crystalline nitride has been employed in an EL device which comprises an alkali earth chalcogen compound as a host material. However, satisfactory luminance and breakdown strength cannot be attained even by such an EL device.
In addition, a transparent electrode layer comprising a crystalline material has not been reported as yet.